In recent years, communication devices like handy phones continue to advance their functions toward multiband communications and combinations with new systems to secure a number of channels and to cope with introduction of new systems such as so-called third generation system and the like due to an upsurge in the number of subscribers in the individual mobile telephone systems. In addition, there is a growing demand for miniaturization and reduction of insertion losses on components used for the handy phones.
In GSM (i.e. Global System for Mobile Communications), which has come into widespread use from Europe to the world, there has been introduced a communication system using 900 MHz band and 1,800 MHz band, and dual-band communication terminals supporting this system are now available in the market. FIG. 11 shows a circuit block diagram of an antenna front-end section of a dual-band handy phone adapted to a combination of GSM (transmission in a range of 880 to 915 MHz and reception in a range of 925 to 960 MHz) and DCS (i.e. Digital Cellular System, for transmission in a range of 1,710 to 1,785 MHz and reception in a range of 1,805 to 1,880 MHz).
In FIG. 11, the antenna front-end section comprises antenna terminal 101, transmission terminals 102 and 103, reception terminals 104 and 105, diplexer 106 for combining and branching GSM transmission/reception signals and DCS transmission/reception signals, switches 107 and 108 for selection between transmission and reception of GSM and DCS services respectively, LPF's 109 and 110 for filtering off high harmonic components of transmission signal of GSM and DCS services respectively, BPF's 111 and 112 having passbands corresponding to the respective receiving frequency bands of GSM and DCS services, and control terminals 113 and 114 of the switches for selection of transmission and reception of the GSM and DCS services respectively.
Surface acoustic wave (“SAW”) filter is an example of components used as BPF's 111 and 112. Switches 107 and 108 for selection between transmission and reception are SPDT (i.e. single-pole double-throw type) switches operable for selecting between transmission and reception in response to a voltage or the like impressed individually on control terminals 113 and 114.
In addition, transmission terminals 102 and 103 are connected externally to transmission circuits including transmission amplifiers 115 and 116, receiving side terminals 104 and 105 are connected externally to reception circuits including LNA's (i.e. low noise amplifiers) 117 and 118 respectively, and antenna terminal 101 is connected to an antenna outside, to constitute the communication device.
As W-CDMA (i.e. Wideband Code Division Multiple Access) employing CDMA (i.e. Code Division Multiple Access) method will be introduced in the forthcoming third generation, it is extremely important industrially to bring out compound terminals for both W-CDMA and GSM services in order to use the existing GSM infrastructure effectively. In this case, it is necessary for any such terminals to operate in a manner that it takes reception of GSM service while making communication with W-CDMA services, and it also takes reception of W-CDMA service while being in reception with GSM at the same time, in order to ensure compatibility with the existing systems.
However, based as it is on the above-discussed structure of the prior art, it is not possible to adapt it for the compound function with the forthcoming third generation systems.